1. Field of the Invention
The present invention generally relates to a method for forming a dielectric layer on a substrate having a recess. In particular, the present invention is directed to a method for forming a dielectric layer free of voids on a substrate having a recess.
2. Description of the Prior Art
A metal-oxide-semiconductor field-effect transistor, MOSFET for short, is a widely used field-effect transistor. According to the polarity of its channel, the MOSFET is divided into the P-type and the N-Type, i.e. PMOS and NMOS. Functionally speaking, PMOS and NMOS each has different threshold voltages, which are determined by the difference of the work function of the gate and the channel material. This can be accomplished by two different metals as the gate materials.
In order to increase the carrier mobility in the channel region to meet different requirements of the PMOS and NMOS, some stress layers of different stresses are respectively formed adjacent to the gate channels of the PMOS and NMOS in order to apply a suitable stress, such as a tensile stress or a compressive stress to the gate channels. For example, a tensile stress is suitable for an NMOS gate channel and a compressive stress is suitable for a PMOS or a gate channel.
However, when a dielectric layer is formed at a border region where stress layers of different stresses are close to each other, voids are also likely to be collaterally formed nearby. These voids may potentially damage the quality and reliability of the dielectric layer.